Bi-directional overrunning clutches are known in which a pair of substantially coaxial hubs are positioned in a housing that is driven by an external drive mechanism. Each hub is adapted to drive a segment of a drive shaft of a wheeled vehicle, one hub driving a left wheel and the other hub driving a right wheel. A plurality of rollers are positioned in an annular space between an internal cam surface of the housing and an outer surface of each of the hubs by a roll cage, each roller being located in a slot in the roll cage, such that wedging engagement of the rollers between the hubs and the cam surface enables the transfer of torque from the housing to the hubs or from one or both of the hubs to the housing.
To facilitate wedging engagement of the rollers when the housing rotates relative to the hubs, it is preferable to index the rollers with respect to the hub. Indexing can be accomplished by creating a frictional interface between a portion of the roll cage and each of the hubs. In an exemplary operation in which the wheeled vehicle starts moving from a stopped condition, the frictional interface causes the roll cage to remain stationary with the hubs when the housing begins to rotate, enabling the rollers to contact the inner cam surface of the housing and wedge between the inner cam surface and the outer surfaces of the hubs.
During deceleration, a similar action can be used to enable regenerative braking, whereby the housing decelerates before the hub and the frictional interface between the roll cage and the hubs causes the roll cage to travel along with the hubs, such that the rollers contact and wedgingly engage between the inner cam surface and the hubs. This same occurrence can happen on a gas or diesel utility vehicle that has EBA (engine braking ability). Consequently, energy dissipated by slowing down the vehicle can be absorbed by the external drive mechanism. However, as a result of drive systems, and specifically differentials, that are typically used with existing clutches, regenerative braking can cause the rollers to shift rapidly back and forth between forward and reverse cam surfaces in the housing, resulting in the driver experiencing a shaking sensation when decelerating, particularly in a turn.
In existing overrunning clutches, the frictional interface often requires a spring to urge two members into frictional engagement, the two members typically including a first member that rotates with the roll cage and a second member that rotates with one of the hubs. However, since the spring may be positioned in contact with an end cap of the housing of the clutch, an undesired frictional interface can be created between the end cap, which rotates at the same speed as the housing, and the spring, which typically rotates with the hub and therefore may be rotating at a different speed than the end cap. The frictional interface between the spring and the end cap may have several undesirable consequences, including accelerated wear which may reduce spring force.
In some clutch designs, the spring is a coil or wound spring, with a left-wound coil spring being used on one side of the clutch and a right-wound coil spring being used on the other side of the clutch, so that the springs do not unwind when the vehicle is in a turn. In these clutches, it is particularly important to reduce or eliminate the frictional interface between the spring and the end cap to ensure proper operation of the clutch. Additionally, it is desirable to replace the left-wound and right-wound springs with a different type of spring to eliminate entirely the risk of unwinding.